Flat telescoped cartridge casing

ABSTRACT

An ammunition cartridge comprising a projectile which is fully telescoped within a flat casing which may be manufactured of identical metal or plastic, glass-reinforced nylon, etc., sections which may be suitably bonded together. The projectile is mountable within a projectile guide tube which is in axial alignment with a booster charge cavity and a percussion primer. The main projectile charge is located within cavities on either side of the projectile tube, which cavities are in communication with the projectile tube via &#39;&#39;&#39;&#39;windows&#39;&#39;&#39;&#39; which are sealed by the surface of the projectile when the latter is in place. The outer walls of the main projectile charge cavities may be provided with apparatus which allows main charge combustion gases to exhaust from the casing and pressurize the entire firing chamber in order to reduce chamber stressing.

United States Patent Goldin 1 FLAT TELESCOPED CARTRIDGE CASING [75] Inventor: Morris Goldin, Orange, Calif.

[73] Assignee: Summa Corporation, Culver City,

Calif.

[22] Filed: Mar. 26, I973 [21] Appl. No.: 344,842

[52] US. Cl. 102/40; 102/38; 102/43 [51] Int. Cl. F421) 5/26 [58] Field of Search 102/38, 40. DIG. 1, 43, 102/43 R, 44; 89/35. 35 A, 33

[56] References Cited UNITED STATES PATENTS 117.338 7/1871 Crary .1 102/40 282.550 8/1883 McLean 102/40 562.535 6/1896 Hurst 102/40 2535624 12/1950 Burney 102/38 2,866,412 12/1958 Meyer et alm. 102/40 2996988 8/1961 Kunz 102/38 3,609.904 10/1971 Scanlon 102/43 P X 3,687.077 8/1972 Goldin r 102/40 3.696.705 10/1972 Hrasbovsky l02/DlG. 1 X

Primary Examiner-Benjamin A. Borchelt Assistant Examiner-H. J. Tudor Attorney. Agent. or Firm-George F. Smyth [57] ABSTRACT An ammunition cartridge comprising a projectile which is fully telescoped within a flat casing which may be manufactured of identical metal or plastic, glass-reinforced nylon, etc., sections which may be suitably bonded together. The projectile is mountable within a projectile guide tube which is in axial alignment with a booster charge cavity and a percussion primer. The main projectile charge is located within cavities on either side of the projectile tube. which cavities are in communication with the projectile tube via windows" which are sealed by the surface of the projectile when the latter is in place. The outer walls of the main projectile charge cavities may be provided with apparatus which allows main charge combustion gases to exhaust from the casing and pressurize the entire firing chamber in order to reduce chamber stress- 4 Claims, 14 Drawing Figures l ill FLAT TELESCOPED CARTRIDGE CASING BACKGROUND OF THE INVENTION In any situation in which fire power is required, whether stationary or mobile, such as an airplane, truck, or foot soldier, the most significant logistics problem must be considered to be the provision of a maximum amount of ammunition with a given fire power for a minimum volume and weight. Most modern weapons employ what has become known as a Standard Brass Cartridge in which a projectile is mounted at the forward end of a brass casing. A propellant powder is mounted within the casing behind the projectile and a suitable booster and primer are positioned at the tail end of the casing. Impact of a firing pin or hammer on the casing in the area of the primer causes ignition and combustion of the primer and the booster charge and then the main charge so that the projectile is driven from the weapon with proper velocity. Similar structure is also in use in which the casing is manufactured of steel or aluminum.

Recent research has shown that the projectile may be partially or fully telescoped within a sleeve of gunpowder and is commonly referred to as a caseless cartridge. An example of a caseless cartridge is described and illustrated in US. Pat. No. 3,687,077, assigned to the Assignee hereof. In that patent, a multi-sided, flat, fully telescoped caseless cartridge is compared to the Standard Brass Cartridge and the Frankfort Arsenal Caseless cartridge which comprises a partially telescoped caseless cartridge, normally round in external configuration. Also, in US. Pat. No. 3,482,516, a fully telescoped caseless cartridge having a round peripheral configuration has been disclosed.

These patent disclosures have made it very apparent to those skilled in the art that a fully telescoped caseless cartridge is clearly superior to the prior art cartridges in rounds per pound and rounds per volume.

Although the above-described advantages are ex tremely important in fire power logistics, it has been found that in some cases, the caseless cartridges either create or are susceptible to very undesirable problems.

Some of the more apparent problems involved with caseless cartridges are production molding difficulties, erosion of the cartridge sleeve by chipping of small parts of the propellant charge sleeve, fouling of the weapon due to an accumulation of the sleeve chippings, vulnerability of the cartridges to external sources of ignition or damage caused by rough handling, and durability and environmental problems relating to humidity, etc. On the other hand, an even more serious problem arises from the fact that some forms of caseless ammunition will cook off at relatively rapid firing rates within approximately rounds. Obviously, the inability of the marksman to stop his weapon from firing can result in very serious and dangerous situations.

On the other hand, the desirable features of the fully telescoped cartridge provide a real incentive to effect some form of compromise in order to achieve the advantages of both the standard cartridges and the caseless cartridges.

In another area of the art of firearms, nearly every attempt at design of a weapon and of ammunition has given consideration to the amount of pressure gener ated in the firing chamber and the rate at which that pressure is dissipated. Each weapon must be designed to absorb the peak pressures generated by the combustion of the propellant charge. With prior art ammunition, combustion pressure builds up at a very rapid rate. rises to a very sharp peak, and then drops off again at a rapid rate. On the other hand, the energy which may be delivered to the projectile is a function of the pressure and, in simplified terms, is equal to the area under the pressure curve. In many cases, the ammunition is designed so that a predetermined amount of energy will be delivered to the projectile in accordance with firing velocity and range requirements. When this energy has been determined, the peak pressure required to obtain the energy is then calculated and the weapon designed to withstand that peak pressure.

It quickly becomes apparent that, in the optimum case, it is desirable to have a low peak pressure with a large area beneath the pressure curve. The theoretically ideal case would be to have an instantaneous pressure rise to a predetermined pressure, a constant pressure for a predetermined period of time, and an instantaneous drop; in other words, a square wave.

Since a gun needs to be designed to absorb the peak pressure, if the peak is lowered while the area beneath the curve is increased, thus achieving the desired energy, the structure of the gun can be significantly lighter while still being able to achieve the same projectile velocity, firing rates, etc., as much heavier weapons.

Accordingly, it has been found to be desirable to develop a cartridge which will produce a combustion pressure as close to a square wave as possible or, at least, which will substantially reduce the peak pressure while maintaining a desirable energy level. Also, it is preferred that the cartridge thus developed be (1 of as low weight as possible, (2) of as small a volume as possible to allow more cartridges to be stored within a given space, (3) easily producible, (4) not subject to erosion, (5) unable to cause firearm fouling, (6) durable and environmentally impervious, (7) not subject to damage because of rough handling, (8) not subject to cook off at normal firing rates, and (9) not vulnerable to ignited or damaged by short exposures to open flame.

SUMMARY OF THE INVENTION The present invention relates to a fully telescoped cased cartridge which has substantially the abovedescribed characteristics. More specifically, the present invention relates to a cartridge which will yield a lower peak pressure generated over a longer period of time than with any known prior art cartridges. In the preferred embodiment of the invention, the cartridge case may be manufactured of any suitable material such as a plastic. With proper design, such a case would be easily produced, impervious to erosion, incapable of fouling a firearm, very durable in storage, transport, and use, and substantially immune to damage caused by mishandling, moisture, etc. Such a case may be produced from simple moldings which may be suitably bonded or welded together.

In order to reduce the volume and the weight of the cartridge, the casing may be formed in a relatively flat configuration, being somewhat rectangular in all cross sections, and having a projectile guide tube extending along the axis throughout a large part of the length thereof. A booster charge and a percussion primer may be axially aligned behind the trailing end of the projectile in order to accomplish the initiation of combustion.

Extending outwardly from either side of the projectile guide tube, the case may define a pair of cavities which extend substantially throughout the length of the casing and into which the main propellant charge may be installed. A pair of windows situated at or near the mid-section of the casing provide communication between the charge cavities and the interior of the projectile guide tube in order to deliver impulse force to the tail end of the projectile and drive it out of the firing chamber and barrel toward its target.

in the copending US. application Ser. No. 43,834, filed June 5. 1970 and assigned to the Assignee hereof, and now US. Pat. No. 3,713,240. a lockless weapon system was disclosed which included a firing chamber of novel construction. In that firing chamber, the front and rear ends of the chamber are held together by a pair of strap members. A cartridge is inserted between the strap members from one side of the firearm and, if necessary, is ejected from between them on the opposite side of the firearm. The chamber is closed by a sliding sleeve which completely surrounds the straps and extends beyond the forward and rear end of the cham her when the latter is closed.

in that firearm, the basic purpose of the straps is to maintain a fixed relative position of the forward and rear ends of the chamber. Since the straps are part of the structure, and since the cartridge must be placed between the front and rear ends of the firing chamber. the straps thus define the cartridge feed and ejection openings.

A sleeve is mounted over the firearm structure for reciprocation relative to the firing chamber. When the sleeve is withdrawn, a cartridge may be fed into or ejected from the chamber but, when the sleeve is properly positioned, it completely surrounds the firing chamber and the straps and serves to close the feed and ejection openings. In order to prevent the escape of the combustion gases, the sleeve cooperates with sealing devices which are mounted either in the sleeve or on the peripheral surface of the firearm at either end of the firing chamber.

Experience has shown that some action must be taken to prevent the powder combustion which occurs in such a lockless weapon system from creating a large pressure differential across the straps, i.e., from the side of the strap adjacent the cartridge to that adjacent the sleeve. If care is not taken, excessive pressure in the firing chamber between the straps will cause the straps to be overly stressed and, possibly. to assume a permanent set. This problem is, of course, overcome when a caseless cartridge is utilized with the firearm since the gas pressure within the cartridge will be transmitted throughout the entire area bounded by the sleeve and the sealing devices, thus causing the pressures on the opposite sides of each of the straps to be substantially equal. When this condition occurs, the straps will not be stressed radially, relative to the firing chamber. and thus cannot assume a permanent set which may interfere with the travel of the sleeve and/or the seating of cartridges in the firing chamber.

Thus it will be realized that ifan encased cartridge is used with the lockless weapon system, some means must be provided to prevent the differential pressure across the strap from becoming too large to allow the strap to return to its normal position after a firing, if the strap changes position at all. Some rather unacceptable methods are to either reduce the charge in the ear tridge or increase the mass (and weight) of the gun.

In order to accomplish this result with the cartridges formed in accordance with the present invention, an area is formed through which gases can pass into and pressurize the chamber. in one form, a deliberate point or line of weakness is formed along the sides at the top and bottom of the cartridge so that some of the combustion gas can escape and pressurize the entire volume within the sleeve at a substantially uniform pressure. Although the combustion within the cartridge occurs at a very rapid rate, the volume within the sleeve will be pressurized and the pressure therein will ultimately flow back through the casing and out through the barrel. in this manner, a portion of the pressure is exerted over a longer period of time and this might be one of several devices which can be employed in an attempt to achieve a lower peak pressure over a longer period of time, ie, a lower peak pressure with the predetermined quantity of energy. in another embodiment. the same results may be achieved by allowing the gases to pass between the interface of an opening and its closure panel in the casing.

The internal configuration of the casing is another device which can be utilized to extend the time over which the pressure is exerted at a lower peak rate. Since the windows connecting the powder cavities to the projectile guide tube are near the mid-section of the casing, and since the powder is arranged so that it extends from the front of the casing to the rear of the casing, it will be realized that a relatively large amount of gas turbulence within the casing will occur, including, for at least part of the powder. a complete reversal of the direction of travel of the gas. Consequently, combustion pressure will be exerted over a longer period of time at a lower peak rate.

Another method of extending the time over which the pressure is exerted and reducing the peak pressure is presently theorized to involve the proper construction of the propellant charge. Initial test results lead to the conclusion that cartridges formed in accordance with the present invention may be provided with a powder charge in the matrix or block form. If the blocks used are coated with different thicknesses of a combustible acrylic material. for example, then the time of combustion ignition of different portions of the charge will vary so that combustion will continue over a greater length of time. As a result, the pressure will not reach as high a peak pressure at any given instant and it will be exerted over a longer period of time, thus providing the same quantity of energy without requiring that the firearm structure be manufactured to withstand high peak pressures.

ln order to produce casings which are as lightweight and as inexpensive as possible, and since the peak combustion pressures are reduced by this invention, it is proposed that in the preferred embodiments the easings be plastic or glass reinforced nylon; however, metal or metal components may be used. Such casings may, for example, be molded in mating sections which are identical, the sections being suitably bonded or welded together at an interface.

Various additional objects, modes, and embodiments of the present invention will become apparent to those skilled in the art upon review of the following detailed description which refers to the embodiments illustrated in the drawings. It will be understood, of course. that the illustrated embodiments are exemplary only and it is the intention that all such other embodiments and modes which may he developed utilizing the concepts of this invention be included in the scope thereof as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I comprises a front elevation of one embodiment of a cartridge formed in accordance with the present invention;

FIG. 2 comprises a horizontal sectional view of the cartridge illustrated in FIG. I as seen along a line IIII therein;

FIG. 3 comprises a longitudinal sectional view of the cartridge illustrated in FIG. I, as seen along a line III- III therein;

FIG. 4 comprises a rear elevation, partly in section. of the cartridge illustrated in FIG. 1;

FIG. 5 comprises a side elevation partly in section, of the cartridge illustrated in FIG. 1 with the element thereof forming a gas expansion passage or line of weakness removed;

FIGS. 6, 7, and 8 comprise a side elevation, top plan view. and rear elevation, respectively, of the removable element of the cartridge of the first embodiment which creates the predetermined lines of weakness therein;

FIG. 9 comprises an isometric illustration. in an exploded view. of the cartridge formed in accordance with the first embodiment;

FIG. 10 comprises a side elevation of a cartridge formed in accordance with a second embodiment of the present invention;

FIG. ll comprises a horizontal sectional view of the cartridge shown in FIG. 10 as seen along a line XIXI thereof;

FIG. 12 comprises a front elevation of the cartridge illustrated in FIG. 10; and

FIGS. 13 and 14 comprise vertical sectional illustrations of the cartridge shown in FIGS. I0 and 11 as seen along lines XIIIXIII and XlV-XIV in FIG. 11, respectively.

DETAILED DESCRIPTION A cartridge formed in accordance with the present invention may be provided with a casing produced from any suitable material. In the preferred embodiments. however, the material utilized may be of plastic or a glass reinforced nylon which is capable of being ultrasonically welded. It will be realized. of course, that any other suitable material may be selected depending upon requirements and availability. However, the preferred materials are very light and may be inexpensively produced by the use of a single set of dies to obtain identical mating halves of the casing.

In any event, the presently preferred embodiment of the invention results in a cartridge casing which approaches the configuration of a rectangular prism, i.e., a six-sided, relatively flat, box-like shape. As shown in FIGS. 1-5, the cartridge casing 21 may be configured so as to have an upper face 23, a lower face 25, a front face 27, a rear face 29, and a pair of side faces 31. The side faces 31 may be substantially identical in configuration and may be curved slightly so as to be fixedly held within the firing chamber ofa gun such as that disclosed in the above-cited copending application Ser. No. 43.834. In other words. the sides 3I of the casing may be shaped so as to cooperate with the internal surface of the slidable sleeve in the Iockless weapon systern.

In FIG. 2, one half of a casing is illustrated which may have an identical half bonded thereto to form a closed casing. At substantially the longitudinal axis of the easing, a bore 33 may be formed into which a projectile 35 (FIG. I only) may be mounted. The bore 33 may be defined by a pair of walls 37 which separate the projectile-receiving bore 33 from a pair of main propellant charge cavities 39 located on either side thereof. The main propellant cavities may extend the full length of the casing and be in open communication with the bore 33 via a pair of windows 41.

Coaxially aligned with and to the rear of the bore 33, a bore 43 may be formed to define a booster charge cavity 45 which may, in turn, be coaxially aligned with and immediately ahead of a stepped percussion primer cavity 47. A tapered bore 49 extending between the bores 33 and 43 may, if desired. be provided to seat the tail end of the projectile.

When the projectile is suitably positioned within the projectile guide tube 33, the sides of the projectile may seal or otherwise fully obturate the windows 41 to prevent any portion of the main charge from escaping from the cavities 39. Of course, in some instances. the projectile may be provided with a rifling band and a bourrelet which may be located one on each side of the windows 41. The close proximity of the periphery of the projectile may still be used to prevent any substantial movement of the main charge.

When the primer is hit by the firing pin. it causes combustion of the booster charge in the cavity 45 and the latter causes the projectile to begin to move out of the cartridge. As the tail end of the projectile moves past the windows 41, the main propellant charge is exposed to the combustion heat generated by the booster charge and begins to burn. The gases from the main propellant charge will not be able to move in a straight line direction since they must travel from the chamber 39 and into the projectile guide tube 33 through the windows 41. The turbulence thus created will improve combustion efficiency by retaining the propellant powder within the chamber. Since chamber pressure is normally higher than the pressure at any given location down the barrel, the powder will be more efficiently burned.

The turbulence generated by the casing is also increased since the gases created by the main propellant charge in the forward portion of the casing must travel toward the rear of the casing, through the windows 41, and then back again toward the front of the casing. Thus. the complete reversal of direction of travel of the gases will increase the turbulence and the length of time during which the useful energy is available.

These features of the cartridge construction serve to help produce a pressure-energy wave which is much closer to being square rather than a sharp peak. This result may be enhanced, if desired. by providing the main charge with slightly different combustion rates so that not all of the burning thereof occurs simultaneously. For example. if a main charge is in the matrix form, various portions thereof can be coated on the exterior with differing thicknesses of a material such as an acrylic. Thus. although every portion of the main charge will burn, the moment of combustion initiation and the rate of combustion will vary slightly and the production of a square pressure-energy wave may be still further enhanced.

When the cartridge formed in accordance with the present invention is to be utilized with a lockless weapon system such as that disclosed and illustrated in the abovecited Patent No. 3,7 l 3,240 the peak pressure generated by the cartridge can be reduced to allow the straps connecting the front and rear of the firing chamber and the other gun components to be made lighter or of lesser strength without damaging the firearm.

Alternatively. the cartridge can be provided with a deliberately located point of weakness so that some of the combustion gases within the cartridge will escape therefrom into the firing chamber and pressurize the entire chamber. If this is accomplished, in a lockless weapon system the pressure differential across the straps will either be zero or at least so low that no undue stresses are created therein. At the same time, the pressure within the firing chamber outside of the cartridge will eventually pass back through the cartridge and out the barrel of the firearm as useful work. In this manner, the turbulence and length of time over which the pressure is exerted are increased still further and serve as another factor in creating a relatively square pressure wave.

In this embodiment of the invention, such deliberate weakness of the cartridge may be formed by providing removable panels 51 such as illustrated in FIGS. 6-8. Each panel is provided with a tapered edge 53 on the upper and lower surface thereof and a tapered edge 55 on the front surface thereof. The tapered edges 53 may be slid or snapped into tracks 59 in the upper and lower walls 23 and 25 of the cartridge as illustrated in FIG. 4. The forward tapered edge 55 of each panel 51 may then be slid into the forward ends of the tracks 59 behind a portion of the side walls 31, as illustrated in FIG. 5.

At the rear of each of the panels, a tab 61 may be provided which, when the panel has been completely slid forward in the tracks 59, will snap in just forward of the end wall 29 so that the panels will be maintained in a fixed position.

During combustion of the main propellant charge in the cavity 39, some of the gases generated thereby will be exhausted from the cartridge past the various interfaces between the panels 51 and the body of the casing. These gases may then pressurize the firing chamber as described previously.

When the pressure within the casing acting on the rear end of the projectile begins to be reduced by expansion thereof, the pressure in the firing chamber will then travel back past the interfaces of the panels 51 and the casing body and allow the pressure exerted through the barrel of the firearm to be continued for a slightly longer period of time.

Thus it will be realized by those skilled in the art that a cartridge formed in accordance with the present invention aids in the production of a relatively square pressure wave, is less susceptible to heat transfer and cook off problems, may be easily produced in a durable and environment resistant form which is not subject to erosion, fouling, or mishandling problems.

With respect to .50 caliber cartridges of this type, having the same muzzle velocity and kinetic energy as Standard Brass Cartridges, the weight per round is approximately less and the volume required per round is nearly 35% less than the brass cartridges. With respect to comparable 7.62 mm cartridges formed (a) in accordance with the present invention and (b) Standard Brass, the present invention cartridges have a weight per round of approximately 25% less, and the number of rounds per pound is approximately 42% greater. Thus, it can be seen that cartridges of this type are clearly advantageous in their use not only from the standpoint of reducing firearm weight and cost, but also in reducing cartridge weight and cost.

Referring now to FIG. 9, an exploded view of the easing illustrated in FIGS. 1-8 has been shown for the sake of illustrating that the casing may be manufactured in two separate, identical pieces which may be joined by any suitable means, such as ultrasonic welding. For this purpose, as shown in FIG. 2, each cartridge half may be provided with one or more locating pins 71 which may be used to cooperate with a similar number of locating bores 73, in the opposite half of the cartridge. After the joining of the cartridge halves has been completed, the projectile, booster, primer, and main charge can be installed and the panels slid into the tracks so as to close the sides of the projectile which is then ready for firing. Thus, the cartridge may be quickly and simply manufactured and ready for firing at a relatively low cost.

Referring now to FIGS. l0l4, there is illustrated a second embodiment of a cartridge formed in accordance with the present invention at 121. As illustrated, the cartridge may be formed with an upper wall 123, a lower wall 125, a forward wall 127, and a rear wall 129. Also, the casing may be provided with side walls 131 which are integral with the main body of the casing. A projectile tube or bore 133 may be defined by a pair of walls 137 which separate the guide tube 133 from main charge cavities 139.

communication between the main charge cavities and the guide tube 133 may be provided by windows 14! which. when a projectile is installed within the guide tube 133, are sealed by the sides of the projectile.

A bore I43, forming a booster charge cavity I45, may be concentrically aligned with the guide tube 133 and in communication therewith through a tapered bore 149 into which the tail end of the projectile may be seated. Similarly, a stepped primer bore 147 may be concentrically aligned and in communication with the booster charge cavity 145.

At the forward end of each of the cavities 139, an ac cess opening 151 may be provided, as shown at the upper portion of FIGS. l1 and 12, which, after the main propellant charge is installed within the cavities, may be closed by snapping a cover 153 therein, as illustrated at the lower portions of FIGS. 11 and 12.

As previously described, if it is desirable to manufac ture the casing of two separate halves, suitable pins 171 and locating bores 173 may be formed in each half of the casing for proper alignment thereof prior to ultrasonic welding.

It should now be apparent that the alternate embodiment of the present invention, as described thus for, is quite similar to that described by reference to FIGS. 1-9. However, the sides of the casing may be formed integral with the main body of the casing and not as separate panels.

If a cartridge formed in accordance with this embodi ment of the invention is to be utilized in a lockless weapon system such as that described in the abovecited copending application, a deliberately positioned line or area of weakness 20] (most clearly shown in FIGS. l0, l3, and 14) may be formed to extend along the edges of the cartridge as illustrated. The lines of weakness 201 are provided by manufacturing the casing to have reduced thicknesses in the areas illustrated. When the main charge is ignited, the combustion gas pressure will rupture the lines of weakness throughout a substantial portion thereof to allow the release of the gas. Since the weakness lines do not extend the entire length of the casing, the casing will not be destroyed but the gas will be allowed to pass out of the casing and then return through it to be exhausted through the barrel in the manner previously described.

lt will now be realized that this embodiment of the invention will produce substantially the same desirable results as the first embodiment previously described.

Thus the applicant has disclosed two embodiments of an inventive concept which may be utilized to lighten the weight and reduce the cost of firearms and cartridges, yielding a true advance in the art. These embodiments are exemplary only and a large number of distinct embodiments will now become apparent to those skilled in the art without exceeding the scope of the claims which define the invention.

I claim: 1. A cartridge casing comprising a projectile guide tube therein having means for seating a projectile in a fully telescoped relationship with said casing, booster charge receiving means in axial alignment with said projectile guide tube,

primer receiving means in axial alignment with said booster charge receiving means,

means, laterally offset from the axis of said projectile guide tube, for receiving a main propellant charge, and

window means, normally completely obturated by a projectile fully seated in said guide tube and located at a position removed from each end of said propellant charge receiving means, providing communication between said guide tube and said main propellant charge receiving means so that combustion of a propellant charge in said propellant charge receiving means commences in two different directions only after projectile movement has occured sufficiently to uncover said window means.

2. The casing of claim 1 including means at the periphery of said casing for releasing pressure generated by main propellant charge combustion to the volume about said casing.

3. The casing of claim 2 wherein said pressure releasing means comprises reduced thickness portions of said casings which are ruptured by such combustion.

4. The casing of claim 2 wherein said pressure releasing means comprises at least one opening therein covered by a releasable cover, about which combustion gases under pressure may pass. 

1. A cartridge casing comprising a projectile guide tube therein having means for seating a projectile in a fully telescoped relationship with said casing, booster charge receiving means in axial alignment with said projectile guide tube, primer receiving means in axial alignment with said booster charge receiving means, means, laterally offset from the axis of said projectile guide tube, for receiving a main propellant charge, and window means, normally completely obturated by a projectile fully seated in said guide tube and located at a position removed from each end of said propellant charge receiving means, providing communication between said guide tube and said main propellant charge receiving means so that combustion of a propellant charge in said propellant charge receiving means commences in two different directions only after projectile movement has occured sufficiently to uncover said window means.
 2. The casing of claim 1 including means at the periphery of said casing for releasing pressure generated by main propellant charge combustion to the volume about said casing.
 3. The casing of claim 2 wherein said pressure releasing means comprises reduced thickness portions of said casings which are ruptured by such combustion.
 4. The casing of claim 2 wherein said pressure releasing means comprises at least one opening therein covered by a releasable cover, about which combustion gases under pressure may pass. 